【leetcode】1161. Maximum Level Sum of a Binary Tree

题目如下：

Given the root of a binary tree, the level of its root is 1, the level of its children is 2, and so on.

Return the smallest level X such that the sum of all the values of nodes at level X is maximal.

Example 1:
Input: [1,7,0,7,-8,null,null]

Output: 2

Explanation:

Level 1 sum = 1.

Level 2 sum = 7 + 0 = 7.

Level 3 sum = 7 + -8 = -1.

So we return the level with the maximum sum which is level 2.
Note:

The number of nodes in the given tree is between 1 and 10^4.

-10^5 <= node.val <= 10^5

解题思路：没什么好说的，依次计算出每一层的值，求出最大即可。

代码如下：

# Definition for a binary tree node.

# class TreeNode(object):

#     def __init__(self, x):

#         self.val = x

#         self.left = None

#         self.right = None

class Solution(object):

    dic = {}

    def recursive(self,node,level):

        self.dic[level] = self.dic.setdefault(level,0) + node.val

        if node.left != None:

            self.recursive(node.left,level+1)

        if node.right != None:

            self.recursive(node.right,level+1)

    def maxLevelSum(self, root):

        """

        :type root: TreeNode

        :rtype: int

        """

        self.dic = {}

        self.recursive(root,1)

        max_val = 0

        res = 0

        for key,val in self.dic.iteritems():

            if max_val < val:

                max_val = val

                res = key

        return res

巴特西

【leetcode】1161. Maximum Level Sum of a Binary Tree

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